Design and Analysis of an Ultraminiaturized FSS Using 2.5-D Convoluted Square Spirals

An ultraminiaturized frequency selective surface (FSS) based on 2.5-D convoluted structure is proposed. 2-D convoluted lines in the form of square spirals are incorporated with vertical vias to give a unit cell size which is only 2.7% of the free-space wavelength at resonance frequency of 2.8 GHz. Transverse-electric (TE) and transverse-magnetic (TM) resonators are combined to synthesize the proposed FSS unit cell resulting in a polarization-independent 2.5-D FSS. Moreover, the designed FSS provides a stable frequency response for incidence angles, up to 75°, for both the TE and TM polarizations. An equivalent circuit model is also developed to provide physical insights into the working mechanism of the proposed FSS. Transmission characteristics of the FSS are analyzed using full-wave simulations and equivalent circuit modeling. A prototype FSS is fabricated and measured utilizing S-band waveguide setup where a good consistency between the measured and simulated frequency responses validates the design process.